These days, nearly every developer is familiar with the benefits of open source code and coding tools. Open source repositories like GitHub and SourceForge provide invaluable resources for those searching for assistance in creating their own applications.

In addition, many of the most popular development tools are available under open source licenses. The last few years have seen an explosion of new tools, particularly in categories like mobile development and JavaScript frameworks. This month we're updating our previous list of open source development tools and highlighting 101 of the very best open source bugtrackers, programming languages, version control systems, frameworks, IDEs, text editors and other tools.

There is such a large and diverse group of open source development tools that we can't possibly include everyone's favorites on our list. If you'd like to call attention to some that didn't get included, feel free to add them to the Comments section below.

API Creation

Apigility claims to be "the world's easiest way to create high-quality APIs." It allows users to get started creating their first API in just seconds, and it works with all PHP frameworks and libraries. Operating System: Windows, Linux, OS X

Designed to be light, fast and flexible, Falcon is a Python framework for building cloud APIs and web app back-ends. Fairly new, its website proclaims that it has been "Unburdening cloud apps for over 2.16 x 10-2 centuries" (that's a little over two years). Operating System: Windows, Linux, OS X

Bugtrackers

This defect-tracking software is very popular with open source projects and is used by organizations like Mozilla, Eclipse, Apache, Red Hat and the Linux kernel project. It tracks bugs and code changes, allows developers to submit and review patches, enables team communication and helps manage quality assurance. Operating System: Windows, Linux, OS X

Cloud9 gives developers access to a cloud-based code editor and Ubuntu workspace. The link above connects users to the hosted service with free and paid plans available; users can also set up their own Web server hosting the IDE using the code from GitHub. Operating System: OS Independent

Dev-C++ supports C and C++, and it includes an integrated debugger, project management, customizable syntax highlighting, code completion, class browser and more. The link above takes you to the original project, but there is also a fork that has been updated more recently on the Dev-C++ Blog. Operating System: Windows

Sponsored by SAP, Dirigible describes itself as an Integrated Development Environment as a Service (IDEaaS). This link connects to the hosted service (which is currently available for free), and the code is available through GitHub. Operating System: OS Independent

One of the most well-known and popular groups of development tools, Eclipse offers IDEs for Java, Java EE, C/C++ and PHP. The Eclipse Foundation also sponsors a whole host of related projects available through the site. Operating System: OS Independent

KDE's development environment boasts full-featured support for C/C++ and some other languages. Although it was developed for the KDE Linux desktop, it also runs on GNOME and other desktops, as well as Windows and Unix. Operating System: Windows, Linux, OS X

Mono describes itself as "an open source implementation of Microsoft's .NET Framework based on the ECMA standards for C# and the Common Language Runtime." It enables rapid development of cross-platform applications. Previously sponsored by Novell, it's now owned by Xamarin. Operating System: Windows, Linux, OS X, iOS, Android

Useful for creating desktop, mobile or Web apps, NetBeans supports Java, HTML5, PHP, C/C++ and several other programming languages. It has won several awards and boasts a large library of plug-ins. Operating System: Windows, Linux, OS X

Designed for C++ development, Utlimate++, or U++, boasts that it can makes rebuilds four times faster than its competitors. It includes a wealth of tools that speed programming include documentation generators, visual designers and a code analyzer. Operating System: Windows, Linux

JavaScript Frameworks and Libraries

Sponsored by Google, this "superheroic" JavaScript framework aims to make it easier to add dynamic content to HTML Web pages. It's embeddable and extensible and works with a wide range of other development tools. Operating System: OS Independent

Chaplin.js is an architecture for Backbone.js applications. It was designed to address some of the limitations of Backbone.js and help developers quickly create single-page Web apps. Operating System: Windows, Linux

This JavaScript framework is all about protecting users' privacy. It allows developers to build applications that encrypt all data stored on the server, without requiring developers to become experts in cryptography. Operating System: OS Independent

Twitter created this lightweight, event-drivien JavaScript framework for use on its own Web apps and has open sourced the code for everyone. It maps behavior to DOM nodes. Operating System: OS Independent

Hammer.js is a JavaScript library for recognizing touch and mouse gestures. It recognizes pan, pinch, press, rotate, swipe and tap gestures by default, and it is very useful for building mobile-friendly Web apps. Operating System: OS Independent

This popular JavaScript library simplifies HTML document manipulation, event handling, animation and Ajax and claims to have "changed the way that millions of people write JavaScript." Its sponsors include WordPress, Famo.us, and IBM. Operating System: OS Independent

Meteor promises to help users "build apps that are a delight to use, faster than you ever thought possible." It claims that its reactive programming model allows Web and mobile developers to accomplish in 10 lines what would otherwise take 1,000. Operating System: OS Independent

This Yahoo Cocktail is a MVC JavaScript application framework that can run on client browsers and in Node.js on servers. It includes tools for local development, internationalization, localization, integrated unit testing and device-specific presentation. Operating System: Linux

Based on Node.js, Node-RED is "a visual tool for wiring the Internet of Things." It makes it easy to connect IoT devices, APIs and online services to invent new things. Operating System: OS Independent

This JavaScript framework wants to help developers build "ambitious Web user interfaces." It aims to simplify development and help developers find more elegant ways around Ajax and the DOM. Operating System: OS Independent

This JavaScript framework wants to "bridge the gap between business and IT" by making it easy to build and deploy applications. It comes in both free and paid versions. Operating System: Windows, Linux, OS X

This cross-platform mobile development environment includes an IDE, an SDK with thousands of device and OS APIs, an MVC framework and cloud-based backend services. It has been used to create more than 76,000 mobile apps deployed on more than 280 million devices. Operating System: Windows, Linux, OS X, iOS, Android

An Apache project, Cordova allows developers to create native cross-platform applications using Web development tools like HTML, CSS and JavaScript. Its APIs allow access to smartphone features like the camera, accelerometer, GPS, etc., and it has been integrated into many other open source projects. Operating System: Windows, Linux, OS X, iOS, Android, Windows Phone, others.

Designed for novices, Game Editor aims to help inexperienced developers learn the basics of programming and create games for nearly any platform. It boasts an intuitive interface, event-driving programming, fast design prototyping and input flexibility. Operating System: Windows, Linux, OS X, iOS, others

A product of Edhouse, iPFaces excels at the creation of form-heavy mobile apps using Web development technologies. It's available in both a free community version and a paid commercial version. Operating System: OS Independent for the developer; creates apps for iOS, Android, BlackBerry, others

JQuery Mobile makes it easy to create HTML 5-based user interfaces for websites being accessed by smartphones and tablets as well as desktops and laptops. Among its noteworthy features is a ThemeRoller that applies a consistent look and feel across sites. Operating System: iOS, Android, BlackBerry, Windows Phone, others

Used by organizations like Massachusetts General Hospital, Harvard University, Brown University, the University of Wisconsin and many others, Kurogo describes itself as "open-source Mobile Optimized Middleware™ for developing content-rich mobile websites and iOS and Android apps." The name comes from a Japanese word for stagehands who are invisible to the audience but allow the stars of the show to shine. Operating System: Windows, Linux, iOS, Android

Designed for use by experienced professionals, this mobile game development platform promises to allow developers to add cloud features to their games in just half an hour. Note that while the platform SDK is free and open source, using the related Moai cloud does incur charges. Operating System: Windows, OS X, iOS, Android, Chrome

This rapid application development framework aims to enable business users and other programming novices to create, deploy and maintain mobile apps. It is based on HTML5 and offers advanced security capabilities, including encryption. Operating System: Android, iOS, BlackBerry

Downloaded more than a million times, PhoneGap is an extremely popular tool for building cross-platform mobile apps with HTML 5, CSS and JavaScript. It is closely related to the Apache Cordova project. Operating System: Window, Linux, OS X

This cross-platform development tool is both an application framework and a UI framework. It supports C++ and a unique language called QML. It's available under an open source license or a commercial license. Operating System: Windows, OS X, Linux

Restkit is an Objective-C framework that simplifies the process of interacting with Web-based REST services. According to the project website, its primary goal is to allow developers "to think more in terms of their application's data model and worry less about the details of sending requests, parsing responses, and building representations of remote resources." Operating System: iOS

THyM stands for "The Hybrid Mobile Project," and it enables cross-platform mobile development through the Eclipse IDE. It also supports Cordova, and it is part of JBoss Developer Studio and Zend Studio. Operating System: OS Independent

Modeling

Downloaded more than 80,000 times, ArgoUML claims to be "the leading open source UML modeling tool." It is useful for creating class, statechart, activity, use case, collaboration, deployment or sequence diagrams. Operating System: OS Independent

Parallel Programming

Also known as TBB, Threaded Building Blocks is a tool that helps developers write C++ programs that take advantage of the processing power in multi-core systems. A commercially supported version is available. Operating System: Windows, Linux, OS X

Programming Languages

First released by Google in 2009, Go is a static language somewhat similar to C but with garbage collection and some dynamic capabilities. The Go website describes it as "a fast, statically typed, compiled language that feels like a dynamically typed, interpreted language." Operating System: Linux, OS X

Created by Microsoft, F# is a cross-platform "functional-first" programming language. The website includes a huge number of tools for learning the language and using it to write applications. Operating System: Linux, OS X

Used by World of Warcraft and Angry Birds, Lua claims to the "leading scripting language for games." Developed by a Brazilian team, the name for this twenty-two-year-old language is the Portuguese word for "moon." Operating System: OS Independent

One of the two most popular programming languages in the world, Oracle-owned Java enables developers to write cross-platform applications. A huge array of related IDEs, libraries and related tools are available. Operating System: OS Independent

Another popular Web language, PHP powers the server side of some of the world's most popular websites. It stands for "PHP:Hypertext Preprocessor," and it is maintained by The PHP Group. Operating System: Windows, Linux, OS X

Known for being easy to learn, Python is a dynamically-typed language that emphasizes speed and code readability. Its core philosophy is expressed in twenty aphorisms, including "beautiful is better than ugly," simple is better than complex," and "special cases aren't special enough to break the rules." Operating System: Windows, Linux, OS X

This programming language is designed specifically for handling statistical computing and graphics. As big data and analytics have become increasingly important for enterprises, R usage has skyrocketed. Operating System: Windows, Linux, OS X

Inspired by Perl, Smalltalk, Eiffel, Ada, and Lisp, Ruby calls itself "a programmer's best friend." While its usage has declined somewhat recently, it's still one of the twenty most popular programming languages. It's dynamic, object-oriented and designed to seem "natural." Operating System: Windows, Linux, OS X

Microsoft first released this JavaScript variant in 2012. It works with JavaScript libraries and compiles to JavaScript code, but adds static typing capabilities and improved scalability. Operating System: OS Independent

Testing

Appium automates the testing of native, hybrid and mobile web apps. It supports both iOS and Android apps and works with most popular development tools, frameworks and languages. Operating System: OS Independent

Calling itself the "Swiss Army knife of testing," SoapUI makes it possible to do functional, regression, compliance, and load tests of applications for nearly any platform. A paid commercial version and training are also available. Operating System: OS Independent

Text Editors

Designed for developers who prefer working in a text editor rather than a full-fledged IDE, ATPad offers a tabbed environment, line numbering, bookmarks, a snippet system, unlimited undo/redo and more. Operating System: Windows.

JavaScript-based CodeMirror makes it possible to embed a text editor in a Web browser. It supports more than 90 languages with autocompletion, code folding, bracket and tag matching, and more. Operating System: OS Independent

Since the 1970s, generations of developers have used Emacs for writing code. It offers content-sensitive editing, syntax coloring, full Unicode support, customization capabilities and a large library of extensions. Operating System: Windows, Linux, OS X

This Java-based text editor supports more than 200 programming languages. It includes a built-in macro language with hundreds of pre-written macros and extensions available. Operating System: OS Independent

For Macs only, this text editor says it wants to bring code and markup into the 21st century. Note that it is open source but not necessarily free; commercial licenses are sold on the site. Operating System: OS X

Vim is a mature text editor with many die-hard fans and a long-time rivalry with Emacs. It's highly configurable and is sometimes called a "programmer's editor" because it has many of the features of full IDEs. It is charityware, so those who use it are asked to donate to an organization that helps needy children in Uganda. Operating System: Windows, Linux, OS X

This fast, lightweight editor is good for just one thing—writing valid XML code. It features syntax highlighting, folding, tag completion, spell and style check and import and export from Microsoft Word. Operating System: Windows, Linux

Version Control

This cross-platform version control system is sponsored by Canonical (the makers of Ubuntu Linux) and is part of the GNU project. It's used by many well-known open source projects, including GNU, Ubuntu, MySQL, Bugzilla, Debian and Inkscape. Operating System: Windows, Linux, OS X

In recent years, Git has taken off as the version control system of choice for many open source and enterprise projects. Source code for thousands of projects that use this distributed version control system are available through GitHub. Operating System: Windows, Linux, OS X

Web Development

Microsoft released this free Web framework under an open source license in 2014. It also allows users to host up to 10 ASP.NET websites for free on its Azure cloud computing service. Operating System: Windows, Linux, OS X.

Designed for programmers and experienced Web developers, Bluefish is a powerful yet lightweight Web editor. Features include fast performance, project support, powerful search and replace capabilities, a snippets sidebar, unlimited undo/redo, spell checker, and support for all of the most common Web programming languages. Operating System: Windows, Linux, OS X

Developed at Twitter, Bootstrap claims to be "the most popular HTML, CSS and JS framework for developing responsive, mobile-first projects on the Web. The website includes a library of sites developed with the tool, including ones for Turbo Tax, Intuit Mint, GeekWire, Instacart, Vizio, NC State University and others. Operating System: OS Independent

Another Twitter project, Bower manages frameworks, libraries, assets, utilities and other packages for websites. It works with a lot of other popular Web development tools. Operating System: OS Independent

Founded by Adobe, Brackets describes itself as "a modern, open source text editor that understands web design." It allows users to develop sites and apps for the browser while working in the browser. Operating System: OS Independent

This Perl MVC Web framework aims to promote rapid development and clean design. It includes an integrated development server for testing and works with nearly all Web servers. Operating System: Windows, Linux, OS X

Award-winning Conditionizr makes it easier to create responsive sites that look great on any device and in any browser. It detects the front end and then serves up the appropriate version of a Website. Operating System: OS Independent

Now more than a decade old, Evolutility simplifies the creation of database-driven apps and Web apps without writing any code. The website includes a number of sample applications to show you how it works. Operating System: Windows

JHipster brings together many popular development tools into one package. It uses Spring Boot for the server side, AngularJS and Bootstrap for the front-end, and Yeoman, Bower, Grunt and Maven to help with the workflow. Operating System: OS Independent

KompoZer promises "easy Web authoring" and includes a file management system and a WYSIWYG editor with an interface similar to Adobe Dreamweaver. It's simple enough for use by newbies but also enables the creation of professional-looking websites. Operating System: Windows, Linux, OS X

This popular PHP framework promises to make Web developers' work easier. It boasts "perfect" security, integrated debugging tools, fast performance, an easy learning curve, a large community and more. Operating System: Windows, Linux

OpenBD claims to be "the world's first truly open source and free GPL Java CFML runtime." It allows developers to create Websites using the ColdFusion Markup Language (CFML) without having to purchase Adobe ColdFusion. Services and support are available through partners. Operating System: Windows, Linux

This "fast, free and fun" framework aims to make it easier for anyone to make browser-based games. It includes Canvas and WebGL renderers, a preloader, three physics systems, a sprite handling system, animation, camera control, device scaling and much more. Operating System: Windows, Linux, OS X, Android, iOS

Ruby on Rails promises "Web development that doesn't hurt." It has been used by tens of thousands of organizations, including Basecamp, Twitter, GitHub and Shopify. Operating System: Windows, Linux, OS X

Foundation doesn't claim to be the most popular or the best, but it does call itself "the most advanced responsive front-end framework in the world." The website adds that it is faster for both developers and end users. Paid support and services are available. Operating System: OS Independent

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